1. Field of the Invention
The present invention relates to a rotor for the comminution of input materials and a device with such a rotor.
2. Description of the Background Art
In the comminution of materials, devices with a grinding unit comprising a rotor have proven to be useful. The rotor is essentially made up of a shaft and rotor discs arranged on it, with the grinding tools distributed over the circumference of the discs. The grinding tools can be made from knives, rigid or swinging suspended hammers, cutting tools or the like. As a rule, the rotor has assigned to it a stator, which is equipped with counter-knives, impact surfaces or screening surfaces, or an additional rotor, the rotor discs of which interact with the rotor discs of the first rotor. The input material is supplied radially to the rotor, where it is picked up by the grinding tools and ground in conjunction with the stator tools or the second rotor.
The materials that can be input into such a generic device are of many types and range from, for example, all types of plastics to sheet metals, textiles and electronic wastes, through composite materials and used tires. Depending on the nature of the input material in terms of size, shape and material properties, the rotor is exposed to high mechanical resistance during the grinding operation, so that the power transmission from the drive shaft to the rotor disc is of great significance.
A modular rotor design with a certain number of rotor discs fastened removably on the shaft plays a great role from the view point of rotor assembly, but also during the replacement of damaged or worn rotor discs, since if necessary the rotor can be disassembled into smaller components, which on one hand are easier to handle and on the other hand can be systematically replaced. Such a rotor design, however, especially in conjunction with a force-locking frictional connection between the drive shaft and the end-positioned rotor discs, requires that the drive force can be transmitted reliably and without slippage from one rotor disc to the next.
From WO 2006/064483 A2, a device for grinding elastomers is known, the grinding unit is formed by two rotors that are provided with corrugations over their circumference. The rotors essentially are each formed from a hollow cylinder, the axial ends of which are screwed together with coaxial supporting discs, which in turn are positioned in a rotationally fixed manner on a driven truncated shaft. The rotor thus has no continuous drive shaft.
A rotor of similar design is known from DE 199 28 034 A1, which corresponds to U.S. Pat. No. 6,237,865, and in which instead of a continuous shaft, likewise only truncated shafts are attached on the front faces of the rotor. Otherwise the rotor is formed from coaxially joined discs which are connected with one another axially over longitudinal bars.
These design types of rotors always prove disadvantageous if an axially compressed design is important because of space conditions. The attachment of the supporting discs to the face of the rotor increases the rotor length without achieving an increase in the effective working area for grinding. In addition, such a design is relatively expensive to manufacture and assemble and in the case of manufacturing and assembly inaccuracies, rapidly leads to imbalance of the rotor and losses of round. Furthermore in the case of overload on the rotor, for example if it is blocked because of unintended foreign body input, considerable damage to the grinding unit takes place, since absolute force locking is produced between the drive side and rotor.
An alternative solution for transmitting the driving power from the shaft to the disc is disclosed in DE 39 30 041 A1. There a continuous drive shaft is formed in the area of the seat of the rotor disc with a hexagonal cross-section. The discs have a centric opening complementary to this, so that power transmission from the shaft to the rotor disc is guaranteed by the form locking. A different type of form locking for power transmission is known from DE 94 22 104 U1. The embodiment described there has a drive shaft with axial grooves on its external circumference, which together with corresponding axial grooves on the inner circumference of the individual discs results in a composite cross-section, into which an adjusting spring is placed.
These two solutions also result in absolute force locking between the drive shaft and the rotor disc, so that in the case of overload on the device, damage to the grinding unit is to be feared. Furthermore, the formation of accurately fitting grooves on the shaft and rotor discs implies a considerable increase in costs for manufacturing and assembly.
Furthermore it is known that the drive force can be transferred from the drive shaft to the rotor disc by frictional connection. Both EP 0 019 542 A1 and U.S. Pat. No. 5,381,973 disclose friction or clamping devices for this purpose, which in each case are arranged in an annular recess on the outside of the front face of the rotor disc and surround the drive shaft, producing a frictional connection. For further power transmission of the torque to the inner rotor discs, both documents disclose that adjacent rotor discs are welded together, in other words all rotor discs are permanently bound to one another and thus form a rigid rotor unit.
U.S. Pat. No. 5,381,973 additionally discloses axial centering pins in the contact area of two adjacent rotor discs, which ensure that the individual rotor discs sit in the exactly identical position to one another on the drive shaft. This is significant when assembling the rotor in that the through holes provided in the outer circumferential area must fit exactly in the axial direction so that later the shafts can be slid in without problems for a swinging suspension of hammers. Furthermore it is suggested that the centering pin be replaced by temporary longitudinal rods until the rotor discs are finally connected together by weld seams.
Although the welding together of the rotor discs results in reliable power transmission of the driving torque into all rotor discs, it has the drawback that all rotor discs form a rigid, non-removable rotor unit which is difficult to handle in the case of disassembly or repairs.